poi 取excel单元格内容时，需要判断单元格的类型，才能正确取出

以下内容非原创，原文链接http://blog.sina.com.cn/s/blog_4b5bc01101015iuq.html

ate String getCellValue(HSSFCell cell) {
        String cellValue = "";
        DecimalFormat df = new DecimalFormat("#");
        switch (cell.getCellType()) {
        case HSSFCell.CELL_TYPE_STRING:
            cellValue = cell.getRichStringCellValue().getString().trim();
            break;
        case HSSFCell.CELL_TYPE_NUMERIC:
            cellValue = df.format(cell.getNumericCellValue()).toString();
            break;
        case HSSFCell.CELL_TYPE_BOOLEAN:
            cellValue = String.valueOf(cell.getBooleanCellValue()).trim();
            break;
        case HSSFCell.CELL_TYPE_FORMULA:
            cellValue = cell.getCellFormula();
            break;
        default:
            cellValue = "";
        }
        return cellValue;
    }